So he wants the Federal Aviation Administration to set minimum seat-size guidelines. The point, Schumer suggested, is to right an injustice: “It’s just plain unfair that a person gets charged for extra inches that were once standard.” In other words: Everyone could soon get a government-mandated upgrade.

It’s a crowd-pleasing proposal that might also have some safety benefits. But like so many alleged giveaways for today’s harried travelers, this one won’t come free.

Over the past decade, airlines have become profitable partly by packing more fliers onto each plane. Although that hasn’t always been comfortable for the passengers, it works in their interest by enabling carriers to offer more affordable flights than ever. Reconfiguring cabins will threaten that model and impose new costs that will be passed onto customers, who might soon be wishing for less legroom.

There’s no question that economy-class passengers have less room these days. Between 1985 and 2014, for example, the widest pitch offered by United Airlines shrunk from 36 inches to 31. Discount carriers like Spirit Airlines have narrowed the space to as little as 28 inches — an unheard-of squeeze three decades ago.

What caused the shrinkage? Competition, and the rise of “low-cost carriers,” which pack more seats into planes, lure customers with cheap fares, and then nickel-and-dime them for things like checked bags and bottled water. They’re popular to complain about, but passengers can’t resist them: They make up 26 percent of the North American airline market and play a crucial role in holding down prices.

According to Airlines for America, a trade group, the average airfare in 2011, including fees, was more than 40 percent below the rate in 1980 in constant dollars. Thanks to the recent decline in oil prices, that trend has likely continued.

So if seat size and fares have shrunk more or less in parallel, what happens if the FAA starts requiring more legroom? Could Spirit be as profitable, and offer fares as cheap, if the distance between its seats was 31 inches rather than 28? Based on the 26-row configuration posted to the website SeatGuru, such a change would likely force the airline to lose at least two rows of seats, along with their associated revenue. With oil prices low, perhaps Spirit could manage such a challenge. But when they bounce back, that extra legroom will surely be a threat to low fares.

In January, the travel website Skift attempted to calculate the cost of additional legroom and recline on a passenger jet flying in the competitive North Atlantic region (for example, London to New York). The conclusion: $33 per inch, or $13.33 per degree of recline. In effect, many economy-class passengers have the option to make that purchase by upgrading to an “economy- plus” seat with six inches of extra legroom for about 18 percent over the price of normal economy, the site estimates. Notably, Skift’s analysis shows that the passenger load factor — basically, the seats occupied by paying customers — in economy- plus cabins averages 36 percent, leading it to conclude that “passengers don’t value extra room as much as low fares.”

Will they value that room if it improves safety? Last year, FAA researchers conceded that they lacked data on whether airplanes with less than 31 inches of pitch can be evacuated safely in an emergency. But with the accident rate for commercial aviation far below that for cars, buses and subways (just 136 fatalities in 3.5 billion passenger journeys in 2015), it’s questionable whether air travelers would be willing to pay a premium for what would likely be a marginal improvement in safety. After all, only 7 percent of travelers regularly buy travel insurance.

Either way, Senator Schumer should remind the flying public that regulators don’t mandate prices. If they start mandating seat sizes, passengers might wish they did.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

This article was written by Adam Minter from Bloomberg and was legally licensed through the NewsCred publisher network.

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